three.js/examples/jsm/nodes/functions/BSDF/BRDF_Lambert.js

import ShaderNode from '../../shadernode/ShaderNode.js';
import { mul } from '../../shadernode/ShaderNodeElements.js';

const BRDF_Lambert = new ShaderNode( ( inputs ) => {

	return mul( 1 / Math.PI, inputs.diffuseColor ); // punctual light

} ); // validated

export default BRDF_Lambert;